Probing the superconducting condensate on a nanometer scale

Superconductivity is a rare example of a quantum system in which the wavefunction has a macroscopic quantum effect, due to the unique condensate of electron pairs. The amplitude of the wavefunction is directly related to the pair density, but both amplitude and phase enter the Josephson current : the coherent tunneling of pairs between superconductors. Very sensitive devices exploit the superconducting state, however properties of the {\it condensate} on the {\it local scale} are largely unknown, for instance, in unconventional high-T$_c$ cuprate, multiple gap, and gapless superconductors. The technique of choice would be Josephson STS, based on Scanning Tunneling Spectroscopy (STS), where the condensate is {\it directly} probed by measuring the local Josephson current (JC) between a superconducting tip and sample. However, Josephson STS is an experimental challenge since it requires stable superconducting tips, and tunneling conditions close to atomic contact. We demonstrate how these difficulties can be overcome and present the first spatial mapping of the JC on the nanometer scale. The case of an MgB$_2$ film, subject to a normal magnetic field, is considered.Comment: 7 pages, 6 figure

The History of the Regulation of Menstrual Tampons

This paper examines the regulation of menstrual tampons in the United States from their introduction to the market some twenty five years ago to the standards that govern them in the twenty first century. After a brief replay of the introduction of the tampon into the US, this paper discusses the background regulatory scheme for such a medical device. Next, this paper traces the development of the federal rules regulating tampons and tampon packaging, as well as the battles fought in courts of law to accomplish this goal. Finally, topics related to tampon regulation are explored, including the debate over tampon ingredient labeling and the preemption of state law by the federal regulation of tampons

Local Tunneling Study of Three-Dimensional Order Parameter in the π\pi-band of Al-doped MgB2_2 Single Crystals

We have performed local tunneling spectroscopy on high quality Mg$_{1-x}$Al$_x$B$_2$ single crystals by means of Variable Temperature Scanning Tunneling Spectroscopy (STS) in magnetic field up to 3 Tesla. Single gap conductance spectra due to c-axis tunneling were extensively measured, probing different amplitudes of the three-dimensional $\Delta_\pi$ as a function of Al content. Temperature and magnetic field dependences of the conductance spectra were studied in S-I-N configuration: the effect of the doping resulted in a monotonous reduction of the locally measured $T_C$ down to 24K for x=0.2. On the other hand, we have found that the gap amplitude shows a maximum value $\Delta_\pi= 2.3$ meV for x=0.1, while the $\Delta_\pi / T_C$ ratio increases monotonously with doping. The locally measured upper critical field was found to be strongly related to the gap amplitude, showing the maximum value $H_{c2}\simeq3T$ for x=0.1 substituted samples. For this Al concentration the data revealed some spatial inhomogeneity in the distribution of $\Delta_\pi$ on nanometer scale.Comment: 4 pages, 3 figure

On the Generalized Kramers Problem with Exponential Memory Friction

The time-dependent transmission coefficient for the generalized Kramers problem with exponential memory friction has recently been calculated by Kohen and Tannor [D. Kohen and D. J. Tannor, J. Chem. Phys. Vol. 103, 6013 (1995)] using a procedure based on the method of reactive flux and the phase space distribution function. Their analysis is restricted to the high friction regime or diffusion-limited regime. We recently developed a complementary theory for the low-friction energy-diffusion-limited regime in the Markovian limit [Sancho et al., cond-mat/9806001, to appear in J. Chem. Phys.]. Here we generalize our method to the case of an exponential dissipative memory kernel. We test our results, as well as those of Kohen and Tannor, against numerical simulations

Importancia del equilibrio del índice omega-6/omega-3 en el mantenimiento de un buen estado de salud: recomendaciones nutricionales

The modification of dietary patterns has led to a change in fatty acid consumption, with an increase in the consumption of -6 fatty acids and a markerd reduction in the consumption of -3 fatty acids. This in turn has given rise to an imbalance in the -6/ -3 ratio, which is now very different from the original 1:1 ratio of humans in the past. Given the involvement of -6 and -3 essential fatty acids in disease processes, the present article examines changes in dietary patterns that have led to the present reduction in the consumption of -3 essential fatty acids, and to study the importance of the -6/ -3 balance in maintaining good health. In addition, an assesement is made of the established recommendations for preventing a poor intake of -3 essential fatty acids, and the possible options for compensating the lack of these fatty acids in the dietLa modificación de los hábitos alimentarios ha llevado a un cambio en el consumo de ácidos grasos, con una aumento de los ácidos grasos -6 y una marcada reducción en el consumo de los ácidos grasos -3. Esto a su vez ha dado lugar a un desequilibrio en la relación -6/ -3, muy diferente de la proporción original 1:1 que tenían los seres humanos en el pasado. Dada la importancia de la relación entre los ácidos grasos esenciales -6 y -3 en el desarrollo de diferentes enfermedades, en el presente artículo se examinan los cambios en los hábitos alimentarios que han llevado a la reducción en el consumo de ácidos grasos esenciales -3, y se estudia la importancia de este equilibrio en el mantenimiento de la salud. Además, se realiza una evaluación de las recomendaciones establecidas para prevenir una deficiencia en la ingesta de ácidos grasos esenciales -3, y las posibles opciones para compensar la falta de esos ácidos grasos en la diet

Andreev reflections on Y1-xCaxBa2Cu3O7-delta evidence for an unusual proximity effect

We have measured Andreev reflections between an Au tip and Y_{1-x}Ca_{x}Ba_{2}Cu_{3}O_{7 - \delta} thin films in the in-plane orientation. The conductance spectra are best fitted with a pair potential having the "d_{x^{2}-y^{2}+is" symmetry. We find that the amplitude of the "is" component is enhanced as the contact transparency is increased. This is an indication for an unusual proximity effect that modifies the pair potential in the superconductor near the surface with the normal metal.Comment: 4 pages, 4 figure

Protein mass-modulated effects in the catalytic mechanism of dihydrofolate reductase : beyond promoting vibrations

This work was supported by NIH research grants GM068036 (V.L.S.) and GM65368 (A.K.), and NSF grant CHE-0133117 (A.K.).The role of fast protein dynamics in enzyme catalysis has been of great interest in the past decade. Recent “heavy enzyme” studies demonstrate that protein mass-modulated vibrations are linked to the energy barrier for the chemical step of catalyzed reactions. However, the role of fast dynamics in the overall catalytic mechanism of an enzyme has not been addressed. Protein mass-modulated effects in the catalytic mechanism of Escherichia coli dihydrofolate reductase (ecDHFR) are explored by isotopic substitution (13C, 15N, and non-exchangeable 2H) of the wild-type ecDHFR (l-DHFR) to generate a vibrationally perturbed “heavy ecDHFR” (h-DHFR). Steady-state, pre-steady-state, and ligand binding kinetics, intrinsic kinetic isotope effects (KIEint) on the chemical step, and thermal unfolding experiments of both l- and h-DHFR show that the altered protein mass affects the conformational ensembles and protein–ligand interactions, but does not affect the hydride transfer at physiological temperatures (25–45 °C). Below 25 °C, h-DHFR shows altered transition state (TS) structure and increased barrier-crossing probability of the chemical step compared with l-DHFR, indicating temperature-dependent protein vibrational coupling to the chemical step. Protein mass-modulated vibrations in ecDHFR are involved in TS interactions at cold temperatures and are linked to dynamic motions involved in ligand binding at physiological temperatures. Thus, mass effects can affect enzymatic catalysis beyond alterations in promoting vibrations linked to chemistry.Publisher PDFPeer reviewe

Eficacia de un programa para el tratamiento del sobrepeso y la obesidad no mórbida en atención primaria y su influencia en la modificación de estilos de vida

Introducción y Objetivos: la modificación de conductas no saludables es fundamental para tratar la obesidad. El objetivo de este estudio fue evaluar los efectos de un programa basado en dieta, ejercicio y apoyo psicológico en la modificación conductual de pacientes con sobrepeso y obesidad tratados en Atención Primaria. Métodos: 60 pacientes con sobrepeso grado II y obesidad grado I-II fueron incluidos en este ensayo piloto. Edad entre 18-50 años. Los pacientes recibieron un programa que combinaba educación nutricional, actividad física y apoyo psicológico. Formato grupal, periodicidad quincenal. Los principales resultados medidos al inicio y 6 meses fueron parámetros antropométricos (índice de masa corporal, porcentaje de masa grasa, perímetro cintura) y de estilos de vida usando el Cuestionario para la valoración de hábitos de vida relacionados con el sobrepeso y la obesidad. Consta de 5 dimensiones: contenido calórico de la dieta (CC), alimentación saludable (AS), ejercicio físico (EF), comer por bienestar psicológico (BP) y consumo de alcohol (CA). La mayor puntuación indica mejores hábitos para CC, AS y EF y peores para BP y CA. Resultados: al final de la intervención mejoraron las escalas CC (2,60± 0,5 vs 3,49± 0,7, p<0,001), EF (2,19± 0,9 vs 3,17± 1,0, p<0,001) y AS (3,04± 0,4 vs 3,43± 0,4, p<0,05) del cuestionario; CA (3,98± 0,7 vs. 4,25± 0,7, p<0,05) y BP (2,82± 1,0 vs. 3,34± 0,7, p<0,001) empeoraron. Conclusión: el programa basado en moderada restricción de la dieta, aumento de actividad física y apoyo psicológico puede mejorar parámetros antropométricos y estilos de vida en pacientes obesos tratados en un centro de Atención PrimariaBackground: Lifestyle intervention is fundamental for obesity treatment. The aim of this study was to evaluate the effects of a program focused on diet, exercise and psychological support on Lifestyle Modification in overweight and obese patients treated in Primary Health Care setting. Methods: 60 patients with grade II overweight and non-morbid grade I-II obesity were included in this pilot clinical trial. Ages ranged from18 to 50 years. They were provided with a program combining nutritional education, physical activity and psychological support. Subjects attended group sessions every 2 weeks. The main outcome measures at baseline and 6 months were body composition parameters (BMI, body fat percentage, waist circumference) and lifestyle intervention using the Questionnaire for the assessment of overweight and obesity related lifestyles at baseline and six months. This questionnaire yields an five dimensions: diet caloric intake (CC), healthy eating (AS), physical activity (EF), searching for psychological well-being eating (BP) and alcohol intake (CA). The higher score indicates better lifestyles for CC, AS, EF and worse for BP y CA. Results: At the end of the intervention the program achieved improvements in Questionnaire related lifestyles subscales: CC (2,60± 0,5 vs. 3,49± 0,7, p<0,001), EF (2,19± 0,9 vs. 3,17± 1,0, p<0,001) and AS (3,04± 0,4 vs. 3,43± 0,4, p<0,05); CA (3,98± 0,7 vs. 4,25± 0,7, p<0,05) and BP (2,82± 1,0 vs. 3,34± 0,7, p<0,001) has got worse. Conclusion: The Program focused on balanced and moderate energy-restricted diets, increased physical activity and psychological support may improve the anthropometric parameters and the Lifestyle intervention in obese patients treated in a primary healthcare center.Este proyecto ha sido becado por el Ministerio de Ciencia e Innovación, a través del Instituto de Salud Carlos III y la Subdirección General de Evaluación y Fomento de la Investigación, en el marco del «Subprograma de Proyectos de Investigación de Evaluación de Tecnologías Sanitarias e Investigación en servicios de salud». Convocatoria 2008 de ayudas de la Acción Estratégica en Salud, en el marco del Plan Nacional de I+D+I 2008-2011 (PI08/90357). Y por la Fundación MAPFRE, a través del programa de Ayudas a la Investigación (2009